Roman physician Galen (129-215) suggested that these numerous animal spirits flowed through hollow tubes from the brain to all parts of the body – what is now known as the nerve impulse. French philosopher and mechanistic physiologist Rene Descartes (1596-1650) later discredited this concept somewhat when he discovered the modern concept now known as the peripheral nervous system, and emphasized nerve conduction in both directions, between sensory centers and muscles. Animal spirits are also known as vital spirits. See also hydraulic model.
ANIMAL SPIRITS: “Animal spirits, a term coined by Galen, were thought to define the life force connecting body and mind – what is now known as the nervous system.”